Crystallization of amorphous titania prepared by hydrolysis of ethoxide was accelerated even by a small amount of water in the vapor phase. The existence of water promoted the change of localized structure of the amorphous titania to anatase structure, which resulted in acceleration of anatase nucleation. The anatase crystals grew in steam by solid-state epitaxial growth, but stopped growing in a short time. The growth of anatase crystals under hydrothermal conditions could be divided into the following two stages: the first stage with fast growth rate by the solid-state epitaxial growth and the second stage with slow growth rate by the dissolution and deposition process.
During constant-rate heating to 350°C in concentrated NaOH solutions, cubic Zr02 crystallized at = 120°C from hydrated amorphous Zr02; these tine cubic Zr02 particles abruptly changed into needlelike monoclinic Zr02 single crystals at 300°C. Crystallization and phase transformation were studied by XRD, TEM, and EPMA. Cubic Zr02 appears to crystallize via collapse of the Zr02'nH20 structure and subsequent slight rearrangement of the lattice. The abrupt formation of monoclinic Zr02 was considered to result when the very tine cubic Zr02 particles coagulated in a highly oriented fashion.
Lithiophorite with a sandwich layered structure, which consists of stacked MnO 6 octahedral sheets and LiAl 2 (OH) 6 octahedral sheets, was prepared from a birnessite-type sodium manganese oxide with a layered structure, by using a hydrothermal soft chemical process. In the first step, lithium-aluminum hydroxide complex ions (Li x Al n (OH) m z+ ) were inserted into the interlayer space of the manganese oxide layers by an ion-exchange reaction. In the second step, the ion-exchanged manganese oxide was hydrothermally treated to polymerize the complex ions in the interlayer space, forming the sandwich layered structure. The formation reaction of the sandwich layered structure was investigated by XRD, TG-DTA, chemical analyses, and FT-IR spectroscopy. Li x Al n (OH) m z+ can be formed by dropping a LiOH solution into an Al(NO 3 ) 3 solution with Li/Al mole ratio ) 2, at 60 °C. A mixed layered phase of manganese oxide with basal spacings of 0.72 and 0.95 nm was obtained after the ionexchange treatment of the birnessite-type manganese oxide with Li x Al n (OH) m z+ solution. The mixed layered phase transforms to a 0.95-nm layered phase which corresponds to lithiophorite, with a sandwich-layered structure, under hydrothermal conditions. If a Keggin ion (Al 13 O 4 (OH) 24 7+ ) solution was used instead of the Li x Al n (OH) m z+ solution, the pure 0.95-nm phase cannot be obtained. In the formation reaction of the sandwich layered structure, the layered structure of the manganese oxide acts as a template under hydrothermal conditions for the two-dimensional polymerization of Li x Al n (OH) m z+ to a LiAl 2 -(OH) 6 octahedral sheet in the interlayer space.
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